Three-dimensionally woven composite blade with spanwise weft yarns

ABSTRACT

A composite blade has a root and a tip in a spanwise direction and a leading edge and a trailing edge in a chordwise direction. The composite blade includes a three-dimensional woven preform having weft yarns and warp yarns. The weft yarns extend in the spanwise direction of the composite blade. The warp yarns interweave the weft yarns and extend in the chordwise direction of the blade.

BACKGROUND

Composite materials offer potential design improvements in gas turbineengines. For example, in recent years composite materials have beenreplacing metals in gas turbine engine fan blades because of their highstrength and low weight. Most metal gas turbine engine fan blades aretitanium. The ductility of titanium fan blades enables the fan to ingesta bird and remain operable or be safely shut down. The same requirementsare present for composite fan blades.

A composite fan blade can have a sandwich construction with athree-dimensional woven core at the center and two-dimensional filamentreinforced plies or laminations on either side. To form the compositeblade, individual two-dimensional laminations are cut and stacked in amold with the woven core. The woven core extends from the root to thetip of the blade and the plies are stacked on either side of the wovencore to form the desired exterior surface profile. The mold is injectedwith a resin using a resin transfer molding process and cured.Alternatively, the composite blade can comprise a three-dimensionalwoven core cured with resin without the two-dimensional filamentreinforced plies.

SUMMARY

A composite blade has a root and a tip in a spanwise direction and aleading edge and a trailing edge in a chordwise direction. The compositeblade includes a three-dimensional woven preform having weft yarns andwarp yarns. The weft yarns extend in the spanwise direction of thecomposite blade. The warp yarns interweave the weft yarns and extend inthe chordwise direction of the blade.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a gas turbine engine having aturbofan.

FIG. 2 is a perspective view of a composite fan blade for the turbofan.

FIG. 3 a is a cross-sectional view of the composite fan blade of FIG. 2taken along line 3 a-3 a.

FIGS. 3 b-3 d are enlarged views of the composite blade of FIG. 3 aillustrating a layer-to-layer angle interlock weave pattern.

FIG. 4 a is a cross-sectional view of the composite fan blade of FIG. 2taken along line 4-4 having a layer-to-layer angle interlock weave and aconstant thickness tip.

FIG. 4 b is a cross-sectional view of the composite fan blade of FIG. 2taken along line 4-4 having a layer-to-layer angle interlock weave and atapered tip.

FIGS. 5 a and 5 b illustrate an alternative weave pattern for thecomposite fan blade.

DETAILED DESCRIPTION

FIG. 1 is a cross-sectional view of gas turbine engine 10, whichincludes turbofan 12, compressor section 14, combustion section 16 andturbine section 18. Compressor section 14 includes low-pressurecompressor 20 and high-pressure compressor 22. Air is taken in throughfan 12 as fan 12 spins. A portion of the inlet air is directed tocompressor section 14 where it is compressed by a series of rotatingblades and vanes. The compressed air is mixed with fuel, and thenignited in combustor section 16. The combustion exhaust is directed toturbine section 18. Blades and vanes in turbine section 18 extractkinetic energy from the exhaust to turn shaft 24 and provide poweroutput for engine 10.

The portion of inlet air which is taken in through fan 12 and notdirected through compressor section 14 is bypass air. Bypass air isdirected through bypass duct 26 by guide vanes 28. Then the bypass airflows through opening 30 to cool combustor section 16, high pressurecompressor 22 and turbine section 18.

Fan 12 includes a plurality of composite blades 32. FIG. 2 illustratesone composite blade 32, which includes leading edge 34, trailing edge36, pressure side 38, suction side (not shown), airfoil 40 (having tip42), root 44 and longitudinal or spanwise axis 46. Airfoil 40 extendsfrom root 44 and includes tip 42. Root 44 is opposite tip 42.Longitudinal axis 46 extends from root 44 to tip 42. The span of blade32 is generally defined along longitudinal axis 46.

FIG. 3 a is a cross-sectional view of composite blade 32 taken alongline 3 a-3 a. As shown, composite blade 32 includes preform 48 andlaminate sections 50. Preform 48 is a three-dimensional woven compositeformed from a plurality of yarns as described further below. Preform 48extends the spanwise length of composite blade 32 from root 44 to tip42. Preform 48 also extends the chordwise width of composite blade 32from leading edge 34 to trailing edge 36. The shape of preform 48generally follows the shape of blade 32.

Laminate sections 50 are positioned on either side of preform 48. Eachlaminate section 50 comprises a plurality of stacked airfoil plies, asis known in the art. Airfoil plies are two-dimensional fabric skins.Elongated fibers extend through the airfoil plies at specifiedorientations to give the airfoil plies strength. For clarity, theindividual airfoil plies of laminate sections 50 are not shown in thefigures.

To form composite blade 32, the plies of laminate sections 50 arestacked on either side of preform 48 in a mold, resin is injected intothe mold, and the mold is cured. Example resins include but are notlimited to epoxy resins and epoxy resins containing additives such asrubber particulates. Alternatively, vapor deposition can be used todeposit a ceramic matrix on the yarn of preform 48 in place of theresin. In another example, the plies of laminate sections 50 can bepreimpregnated composites, (i.e. “prepregs”) such that resin is notdirectly added to the mold. In a further example, composite blade 32 isformed by preform 48 without laminate sections 50. In this example,preform 48 is placed in the mold, injected with resin and cured to formcomposite blade 32.

As described above, preform 48 is a three-dimensional woven compositeformed by a plurality of yarns. FIGS. 3 b-3 d are enlarged views ofpreform 48 of FIG. 3 a having a layer-to-layer angle interlock weave andincluding warp yarns 52, weft yarns 54, surface weaver yarns 56 and warpstuffer yarns 58. The layer-to-layer angle interlock weave patternillustrated in FIGS. 3 b-3 d comprises three planes that are repeatedalong the spanwise axis of preform 48. Weft yarns 54 extend in thespanwise direction, and warp yarns 52 extend in the chordwise directionand interweave weft yarns 54.

FIG. 3 b illustrates a first plane of the layer-to-layer angle interlockweave, FIG. 3 c illustrates a second plane and FIG. 3 d illustrates athird plane. The first plane shown in FIG. 3 b includes warp yarns 52 a,52 b, 52 c and 52 d (referred to generally as warp yarns 52) and weftyarns 54. Warp yarns 52 extend in a horizontal (or chordwise) directionbetween leading and trailing edges 34 and 36 of preform 48. Weft yarns54 are placed at a 90 degree angle to the direction of warp yarns 52 andare aligned in a spanwise direction of preform 48. Weft yarns 54 extendbetween root 44 and tip 42 of preform 48.

Weft yarns 54 are shown distributed in ten columns (C1-C10). Each columnC1-C10 contains the same number of weft yarns 54. Warp yarns 52interlock weft yarns 54 with a layer-to-layer angle interlock weave.Warp yarns 52 can have a small angle α (such as between about 5 degreesand about 10 degrees), a large angle (such as between about 35 degreesand about 70 degrees) or any angle in-between. In the layer-to-layerangle interlock weaving pattern shown, warp yarns 52 interlock withevery second weft yarn column in the chordwise direction. For example,warp yarn 52 a is woven from the top of the first weft yarn 54 from thetop of column C4 to under the second weft yarn 54 in column C6 to overthe first weft yarn 54 in column C8 over the length of five columns.Warp yarns 52 undulate over and under at least one layer of weft yarns54 to hold the weave together. Because warp yarns 52 weave, they havecrimp angle α and are not straight. Crimp angles α create chordwiseundulations in warp yarns 52 and decrease the stiffness properties inthat direction. The magnitude of crimp angle α affects the stiffness andstrength properties in both the inplane and through-thicknessdirections. For example, a larger crimp angle results in a largerdecrease in inplane strength and stiffness properties in that directionbut provides a larger increase in through-thickness stiffness andstrength properties.

FIG. 3 c illustrates the second plane of the layer-to-layer interlockweave, which includes warp yarns 52 e, 52 f, 52 g and 52 h (referred togenerally as warp yarns 52), weft yarns 54 and surface weaver yarns 56.The second plane of FIG. 3 c is similar to the first plane of FIG. 3 bexcept warps yarns 52 are shifted to the right by two columns. Thus, theinterlocking of warp yarns 52 and weft yarns 54 occurs at differentlocations in the first plane and the second plane. Surface weaver yarns56 weave the edges of preform 48 together to maintain the integrity ofthe weave.

FIG. 3 d illustrates the third plane of the layer-to-layer angleinterlock weave. FIG. 3 d includes weft yarns 54 and warp stuffer yarns58 a, 58 b, 58 c and 58 d (referred to generally as stuffer yarns 58).Stuffer yarns 58 extend in the chordwise direction between weft yarns54. Stuffer yarns 58 increase the stiffness and strength in thedirection that warp yarns 52 extend (i.e. chordwise direction). Stufferyarns 58 do not interweave with weft yarns 54 and therefore do notexperience the crimp angle of warp yarns 52. Because stuffer yarns 58are generally straight, they provide better stiffness properties.Additionally, stuffer yarns 58 provide additional control over the ratioof yarns in the spanwise direction to the yarns in the chordwisedirection of the weave.

Warp yarns 52, weft yarns 54, surface weaver yarns 56 and stuffer yarns58 of preform 48 are formed from bundles of fibers. Example fibers foryarns 52, 54, 56 and 58 of preform 48 include but are not limited tographite fibers, glass and glass-based fibers, polymeric fibers, ceramicfibers (such as silicon carbide fibers) and boron fibers andcombinations thereof. Each individual yarn 52, 54, 56, 58 has a constantnumber of fibers extending the length of the yarn 52, 54, 56, 58. Thefilament count of yarns 52, 54, 56, 58 is referred to as the yarn size.It is noted that in an untensioned state, the yarn size is proportionalto the diameter of the yarn. The larger the yarn size, the larger thediameter of yarn 52, 54, 56, 58. During the weaving process, yarns 52,54, 56, 58 can become elliptical in cross-sectional shape or may have anon-circular cross-sectional shape. As used in this disclosure, yarndiameter refers to the diameter of the yarn prior to the weavingprocess. It is recognized that yarns 52, 54, 56, 58 may not have acircular cross-sectional shape following the weaving process.

The number of weft yarns 54, warp yarns 52, surface weaver yarns 56 andstuffer yarns 58, the spacing between weft yarns 54, the spacing betweenwarp yarns 52, the weave pattern and the repetition of the warp yarnplanes are provided for example only. For example, a layer-to-layerangle interlock weave can be made using four repeating warp yarn planesin which the warp yarns are shifted one column to the right in eachsuccessive plane and/or the stuffer yarn planes and the surface weaveryarns are omitted. Additionally, a layer-to-layer angle interlock weavecan be constructed using weft yarn columns that are staggered such thateach even numbered weft yarn column has one less weft yarn than the oddnumbered weft yarn column. Also, for example, preform 48 can have anythree-dimensional weave pattern such as but not limited to alayer-to-layer angle interlock weave, a through-thickness angleinterlock weave (as described further below) or an orthogonal weave.Various yarn sizes of yarns 52, 54, 56 and 58, number of yarns 52, 54,56 and 58 and weaving patterns can be used without departing from thescope of this invention.

Warp yarns 52 and weft yarns 54 are woven on a loom to produce preform48 as an integrally woven three-dimensional piece. Preform 48 isintegrally woven as a single three-dimensional piece. Preform 48 is notcomprised of a plurality of separate layers that are interwoven. In theweaving process, warp yarns 52 are drawn through an opening in a wirecalled a heddle whose motion can be controlled either by a harness or bya programmable loom head. The mechanism in the loom head canindependently control the vertical motion of each heddle, such as on aJacquard loom. Weft yarns 54 are inserted through warp yarns 52 from theside of the loom during the weaving process, and warp yarns 52 are wovenaround weft yarns 54. The motion of the heddles determines the weavepattern.

In preform 48, weft yarns 54 extend in the spanwise direction and warpor weaver yarns 52 extend in the chordwise direction and interweave weftyarns 54. FIG. 4 a is an enlarged cross-sectional view of tip 42 ofcomposite blade 32 taken along line 4-4 of FIG. 2. As shown in FIG. 4 a,preform 48 can have a relatively constant thickness and laminationsections 50 can be placed on either side of preform 48. Preform 48includes warp yarns 52 and weft yarns 54. Warp yarns 52 are illustratedin rows R1-R10. As described above, warp yarns 52 extend in thechordwise direction along composite blade 32. Warp yarns 52 in rowsR1-R10 have the same yarn size as measured by filament count. That is,warp yarns 52 of tip 42 have about the same diameters. Weft yarns 54extend in the spanwise direction. Weft yarns 54 can also have the sameyarn size as measured by filament count. FIG. 4 a illustrates alayer-to-layer angle interlock weave pattern comprised of four repeatingplanes of warp yarns 52. Each plane has a weave pattern similar to thatshown in FIG. 3 b and warp yarns 52 are moved one weft column to theright in each successive plane. To simplify FIG. 4 a, surface weaveryarns 56 and warp stuffer yarns 58 are not shown. One skilled in the artwill recognize that surface weaver yarns 56 and warp stuffer yarns 58 ofFIGS. 3 c and 3 d, if present, also extend in the chordwise direction.

FIG. 4 b is an alternative enlarged cross-sectional view of tip 42 ofcomposite blade 32 that has a weave pattern similar to that shown inFIG. 4 a except now tip 42 of preform 48 has a tapered shape. Thetapered shape of tip 42 is formed by warp yarns 52. The yarn sizes asmeasured by filament count of warp yarns 52 decrease in the spanwisedirection with increasing distance from root 44. The yarn sizes of warpyarns 52 in the same row, such as row R1, are the same. The yarn sizesof warp yarns 52 in different rows can be varied such that warp yarns 52in row R1 have a smaller yarn size than warp yarns 52 in row R6.Reducing the yarn size of warp yarns 52 reduces the thickness of preform48 and creates the tapered shape. Weaving preform 48 in the chordwisedirection enables warp yarns 52 having smaller yarn sizes to be usedwhere preform 48 is narrower and larger yarn sizes where preform 48 isthicker.

The number of warp yarns 52 in the spanwise direction of preform 48 canalso be reduced with increasing distance from root 44. Reducing thenumber of warp yarns 52 is another factor that can be adjusted to changethe thickness of preform 48. For example, there are four warp yarns 52in row R1 and six warp yarns 52 in row R7. Weaving preform 48 in thechordwise direction enables carrying only the number of warp yarns 52necessary for the thickness in that region. Extra or unnecessary warpyarns 52 are not carried. This eliminates waste of yarn. As describedabove, during the weaving process, warp yarns 52 extend in the chordwisedirection while weft yarns 54 are passed back and forth in the spanwisedirection through sheds formed in warp yarns 52. The number of warpyarns 52 in the chordwise direction can be decreased to reduce thethickness of a region of preform 48, such as in tip 42, or can beincreased to increase the thickness of a region of preform 48, such asat root 44. The yarn size of warp yarns 52 in the chordwise direction,the number of warp yarns 52 in the chordwise direction or the yarn sizeand number of weft yarns 54 in the spanwise direction can be adjusted tocontrol the thickness of preform 48.

Weft yarns 54 extend in the spanwise direction. The yarn size asmeasured by filament count is constant along the length of a specificweft yarn. As shown in FIG. 4 b, weft yarns 54 can be dropped as thenumber of warp yarns 52 is reduced. For example, there are seven weftyarns 54 at a location between root 44 and tip 42 and five weft yarns 54at tip 42. Surface weaver yarns 56 and warp stuffer yarns 58 are notshown in FIG. 4 b to simplify the figure. One skilled in the art willrecognize that, if present, surface weaver yarns 56 and warp stufferyarns 58 of FIGS. 3 c and 3 d extend in the chordwise direction withwarps yarns 52.

As described above, preform 48 is not limited to a layer-to-layer angleinterlock weave pattern. FIGS. 5 a and 5 b illustrate an alternativethrough-thickness angle interlock weave pattern. This through-thicknessangle interlock weave pattern comprises two planes that repeat along thespanwise axis of preform 48. FIG. 5 a illustrates a first plane of thethrough-thickness angle interlock weave pattern which includes warpyarns 52 a, 52 b, 52 c, 52 d, 52 e and 52 f (referred to generally aswarp yarns 52) and weft yarns 54. Warp yarns 52 extend in the chordwisedirection from leading edge 34 to trailing edge 36. Weft yarns 54 arearranged in columns C1-C10 and extend in the spanwise direction betweenroot 44 and tip 42.

In the through-thickness angle interlock pattern, warp yarns 52 a, 52 b,52 c, 52 d, 52 e and 52 f are woven through the same plane. Warp yarns52 interlock with the first and last weft yarns 54 of columns C1-C10.Each warp yarn 52 is woven through the entire thickness of preform 48from pressure side 38 to suction side 47. Similar to that describedabove with respect to the layer-to-layer angle interlock weave pattern,warp yarns 52 have crimp angles because they are woven around weft yarns54. The crimp angles of warp yarns 52 decrease the inplane stiffness andstrength of preform 48 in the chordwise direction. In comparison, weftyarns 54 are generally straight and do not have the crimp anglesexperienced by warp yarns 52. Thus, weft yarns 54 do not experiencedecreased structural stiffness and strength following the weavingprocess.

FIG. 5 b illustrates the second plane of the through-thickness angleinterlock weave pattern, which includes weft yarns 54 and warp stufferyarns 58. Weft yarns 54 extend in the spanwise direction, and stufferyarns 58 extend in the chordwise direction from leading edge 34 totrailing edge 36. Stuffer yarns 58 provide additional stiffness in thechordwise direction.

Regardless of the weave pattern, preform 48 is woven in the chordwisedirection so that weft yarns 54 extend in the spanwise direction andwarp yarns 52 extend in the chordwise direction and interweave weftyarns 54. Weaving preform 48 in the chordwise direction results inincreased stiffness and strength properties in the spanwise direction.Increased stiffness and strength properties in the spanwise direction isparticularly important in airfoil 40 which is subjected to stresses andstrains during normal operation and during impacts by foreign objects.Weaving preform 48 in the chordwise direction aligns weft yarns 54 inthe spanwise direction and warp yarns 52 in the chordwise direction.Weft yarns 54 are relatively straight and thus have better structuralproperties such as stiffness and strength properties. In comparison,warp yarns 52 have a crimp angle due to interweaving and thus havereduced structural properties. Weaving preform 48 in the chordwisedirection aligns weft yarns 54, which have better structural properties,along the spanwise direction where stiffness and strength are moreimportant and aligns warp yarns 52, which have decreased structuralproperties, along the chordwise direction where stiffness and strengthare less important.

Weaving preform 48 in the chordwise direction also avoids limitations onthe number and yarn size of the yarns extending in the spanwisedirection. As described above, when weaving in the chordwise direction,warp yarns 52 are fed through openings in heddles which are controlledfrom the head of a loom, and weft yarns 54 are inserted through shedsformed in warp yarns 52. The number of warp yarns 52 is limited by thecapacity of the head of the loom. For example, in a Jacquard head, thenumber of warp yarns 52 is limited by the number of heddles that extendfrom the head through which warp yarns 52 are threaded. Weft yarns 54are fed from the side of the weaving loom and thus are not limited inyarn size or number by the loom. When preform 48 is woven in thechordwise direction, weft yarns 54 extend in the spanwise direction suchthat the yarns in the spanwise direction (i.e. weft yarns 54) can belarger in number than the loom head may be able to accommodate. The useof more yarns enables smaller yarns sizes to be used to cover the sameacreage.

Additionally, weaving preform 48 in the chordwise direction reduces theamount of wasted yarns because unnecessary yarns are not carried thelength of preform 48. When preform 48 is woven in the chordwisedirection, weft yarns 54 can be added or dropped as necessary to changethe thickness of preform 48 along the length of preform 48 in thespanwise direction. The span of each weft yarn 54 in the spanwisedirection can be controlled by how the weft yarn 54 is passed throughthe shed of warp yarns 52. The passing of a weft yarn 54 through warpyarns 52 is also known as a flight. Weft yarns 54 are inserted throughthe side of the loom and are not required to extend the entire span ofpreform 48. That is, the flight of each weft yarn 54 can be controlledso that weft yarns 54 only extend a specified length in the spanwisedirection.

Further, weaving preform 48 in the chordwise direction enables thecorrect number and yarn size of warp yarns 52 to be used in each regionof preform 48. As suggested by FIG. 4 b, the thickness of preform 48 inthe through-thickness direction can change over the span of preform 48from root 44 to tip 42. For example, preform 48 can have a dovetail root44 that is between about 5.1 cm (2 inches) and about 7.6 cm (3 inches)thick and tip 42 that is less or equal to about 0.6 cm (0.25 inch)thick. When weaving in the chordwise direction, individual warp yarns 52extend in the chordwise direction from leading edge 34 to trailing edge36. Warp yarns 52 are stacked in the spanwise direction. In the spanwisedirection, the yarn size and number of warp yarns 52 can be changed totailor the thickness of preform 48. Only the size and number of warpyarns 52 that are needed are carried along preform 48. Weaving preform48 in the chordwise direction prevents carrying unnecessary warp yarns52 the length of preform 48.

Weaving preform 48 in the chordwise direction also increases the ease ofchanging weave patterns within preform 48. Preform 48 may not have thesame weave pattern throughout. Instead, the weave pattern of preform 48can be changed in the spanwise direction to further tailor theproperties of preform 48. For example, a low angle layer-to-layer angleinterlock weave pattern, such as a weave pattern having crimp angle αbetween about 5 and about 10 degrees, can be used in airfoil 40 while alarge angle layer-to-layer angle interlock weave pattern, such as aweave pattern having crimp angle α between about 35 and about 70degrees, can be used in root 44. The larger crimp angle α increases thethrough-thickness stiffness and strength properties in root 44, andimproves the ability of preform 48 to withstand stresses from operationand foreign object strikes.

When weaving in the chordwise direction, warp yarns 52 can be segregatedinto different regions in the spanwise direction and different weavepatterns can be applied to each region. Because warp yarns 52 are wovenin the chordwise direction, the same weave pattern is applied along thechordwise direction of preform 48 such that the weave pattern at theleading edge and the trailing edge of a given chord is the same, whilethe weave pattern can be changed along the spanwise direction such thatthe weave pattern at the root and the tip may be different. When weavingpreform 48 in the chordwise direction, the weave patterns and theregions in which these patterns are to be applied are determined at thestart. The weave patterns of preform 48 are not changed during theweaving process. Instead, the different weave patterns are started alongpreform 48 at the beginning of the weaving process and are carried outin the chordwise direction throughout the process. Thus, themanufacturing process is simplified.

In summary, weaving preform 48 in the chordwise direction compared toother weaving methods, such as weaving preform 48 in the spanwisedirection, produces an improved preform 48. For example, weaving preform48 in the chordwise direction provides more control over the stiffnessand strength properties of preform 48. Weaving preform 48 in thechordwise direction also reduces waste and simplifies the manufacturingprocess.

While the invention has been described with reference to an exemplaryembodiment(s), it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiment(s) disclosed, but that theinvention will include all embodiments falling within the scope of theappended claims.

The invention claimed is:
 1. A method of forming a composite blade, themethod comprising: forming a three-dimensional woven core, the step offorming the three-dimensional woven core comprising: extending warpyarns in a chordwise direction of the woven core; pulling the warp yarnsapart to form a shed extending in a spanwise direction; passing a weftyarn in the spanwise direction through the shed formed by the warpyarns; and moving the warp yarns after weft yarn is passed through theshed to interlock the weft yarn and the warp yarns; and curing thethree-dimensional woven core to form the composite blade.
 2. The methodof claim 1 and further comprising: varying the yarn size as measured byfilament count of the warp yarns in the spanwise direction.
 3. Themethod of claim 2, wherein the step of varying the yarn size of the warpyarns comprises decreasing the yarn size of the warp yarns withdecreasing distance to a tip of the woven core.
 4. The method of claim 1and further comprising: stacking a plurality of plies on a suction sideof the three-dimensional woven core prior to the step of curing thethree-dimensional woven core.
 5. The method of claim 1 wherein the stepof passing the weft yarns through the shed formed by the warp yarnscomprises: passing the weft yarns through the shed formed by the warpyarns to form a layer-to-layer angle interlock weave pattern.
 6. Themethod of claim 1 wherein the step of passing the weft yarns through theshed formed by the warp yarns comprises: passing the weft yarns throughthe shed formed by the warp yarns to form a through-thickness angleinterlock weave pattern.
 7. The method of claim 1 wherein the step ofpassing the weft yarns through the shed formed by the warp yarnscomprises: passing the weft yarns through the shed formed by the warpyarns to form an orthogonal interlock weave pattern.